1. Field of the Invention
This invention relates to an electric vehicle which is provided with direct-drive and outer-rotor type motor wheels adapted to be directly rotated by a motor and symmetrically disposed longitudinally and laterally.
2. Description of the Prior Art
In recent years, the electric vehicle using battery electricity as a power source and a motor as a drive source has been attracting attention because of such merits as low air pollution, low noise, and easy control, etc.
The conventional electric vehicle is of the double driven axles type which mount mutually independent the wheels and the motors. For the purpose of ensuring smooth and accurate performance of such operations as transmitting the rotation of the motor to the wheels and altering the rotation numbers of the laterally opposite wheels thereby enabling the vehicle to turn a corner, the vehicle of this type inevitably requires use of power transmission devices such as a reduction gear and a differential gear (Japanese Utility Model Application Disclosure SHO No. 47(1972)-18,010) and accessorial devices such as a drive shaft, etc. for interlocking the power transmission devices with the wheels (Japanese Utility Model Application Disclosure SHO No. 48(1973)-38,506).
These power transmission devices and accessorial devices, however, entail not only an addition to the weight of the vehicle body but also a sacrifice of the efficiency of power transmission and consequently have the possibility of increasing the vehicle's energy comsumption and decreasing the vehicle's travelling distance between chargings of its batteries (referred to as "range"). As is widely known particularly in the case of the electric vehicle, the fact that the range is short constitutes one major cause for preventing the electric vehicle from finding widespread acceptance.
Recently, a vehicle using the direct-drive type motor wheels for the purpose of eliminating the aforementioned power transmission devices such as a reduction gear, a differential gear, and a drive shaft, etc. thereby improving the efficiency of powwer transmission and decreasing the weight of the vehicle body has been introduced. These direct-drive type motor wheels, which directly transmit the motor torque to the wheels, fall under two types; those having the wheels mechanically interlocked with the motor (Japanese Utility Model Application Disclosure SHO No. 54(1979)-21,312 and U.S. Pat. No. 3,937,293, for example) and those having motors incorporated in the wheels (Japanese Patent Application Disclosure SHO No. 52(1977)-22,214 and U.S. Pat. No. 4,021,690, for example).
The motor wheels of the former type having the wheels interlocked with the motor have the possibility of increasing the weight of the vehicle body and decreasing the range because they inevitably enlarge the size of the motor wheel in the axial direction and require thick solid rotary shafts of motors to be provided as axles. The whole structure of the motor wheels gains in complexity because it inevitably incorporates therein mechanisms for supporting the rotary shafts and power cables for supply of electricity to the motors. The motors are cooled only with difficulty. Problems also arise as to the operational efficiency with which the motor wheels are assembled and the ease with which the motor wheels are given required maintenance and inspection.
The motor wheels of the latter type having motors attached to the wheel discs pose problems similar to those of the former type because of inevitable use of thick solid rotary motor shafts as axles and consequent complication of the whole construction of the motor wheels. They raise an additional problem that since the motors are disposed inside the wheels, the work of cooling be performed on the motors is liable to expose the motor interiors to dusty ambient air and degrade the durability of the motor wheels due to the contamination by dust.
The double driven axles type electric vehicle mentioned above has motors disposed inside the axles and has shafts of the motors interlocked with the axles by a chain or gears. The batteries as a power source for the motors are mounted on the front and rear parts of the chassis of the vehicle.
The control device for controlling the rotation of the motors is disposed in the front central part of the chassis of the vehicle. This control device is adapted to receive a signal issued from a steering wheel, an accelerator pedal, or a brake pedal at the operator's discretion and, based on this signal, control the travelling condition of th electric vehicle.
In all the signals, the signal issued from the accelerator pedal serves as the reference signal for the control device to compute the torque of the motor. The control device controls the electric current flowing from the batteries to the motors in such a manner that the motors will be caused to rotate with the torque computed in accordance with the reference signal. The motive power generated by the electric current controlled as described above is transmitted via the reduction gear to the wheels and spent there in driving the electric vehicle.
In the electric vehicle of this kind, the batteries are disposed separately in the front and rear parts of the electric vehicle in due consideration of balanced weight distribution. The control device, however, is disposed approximately in the central part of the electric vehicle. The central position selected for the location of the control device is a necessary consequence of the consideration paid to effective use of space and to the ease with which the operator manipulates the control device for impartation of a necessary operating signal.
In the electric vehicle, since the motors as a drive source are attached to the rear wheels, the power lines (the lines for connecting the batteries to the control device and the control device to the motors) inevitably have long distances of distribution. Further, since the power lines are thick copper wires, the total weight of the power lines is naturally heavy.
The conventional electric vehicle, therefore, entails an increase in the weight of the vehicle body and a decrease in the range. The power lines suffer from drop of voltage and loss of electricity in transit. Owing to the drop of voltage and the heavy weight of power lines, the electric vehicle is inevitably compelled to experience a decline in the capacity for acceleration.
The inventor's diligent study directed to elimination of the drawbacks inherent in the conventional electric vehicle as described above, specifically to development of a motor light and compact, capable of manifesting a large output, and optimal for an electric vehicle, has culminated in the development of an electric vehicle which enhances the merits of the direct-drive system, i.e. simplification of the power transmission mechanism and reduction in weight of the entire vehicle body and, at the same time, permits perfect solution of the demerits of the system, i.e. undesirable enlargement of the motor wheels in the axial direction and difficulty involved in the assembly of the entire vehicle body.
The first object of this invention is to provide an electric vehicle which is furnished with direct-drive and outer-rotor type motor wheels contributing to the simplification of the power transmission mechanism and the reduction in weight of the entire vehicle body and fulfilling the dimensional reduction of motor wheels in the axial direction and the facilitation of the work of assembly of the entire vehicle body.
The second object of this invention is to provide an electric vehicle which enables the motors for the motor wheels to be effectively cooled with ease.
The third object of this invention is to provide an electric vehicle which has batteries for supply of electricity to the motor wheels and a control device for control of the motor wheels disposed at positions fit for shortening the total distance of distribution of power lines and decreasing the weight of the vehicle body.